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Can 5G Backhaul Itself?

Yes, there is a parallel between 5G and the movie Inception, but you'll have to stick with me here because we're going to get a bit technical. But I promise it will be worth it, in the end (and hopefully the end of this article will be more satisfying than the spinning top at the end of Inception).

Let's start at the beginning: 5G is all about a new wireless technology that transmits data really fast between a cell tower and a phone, right? That's true, but equally important to 5G is what that cell tower is connected to -- that's called backhaul. After all, it's that backhaul connection that plays a big role in how your phone ultimately reaches Facebook's servers or Netflix's CDN.

Most of the time, at least in this country, that cell tower routes (backhauls) the traffic it collects within its coverage area through a fiber running between the tower and a nearby switching center. Once the traffic hits that switching center, it's then routed to its destination along the nation's core Internet backbone. Think of it like driving around a city until you get onto the interstate.

Now here's where Inception kicks in: What if that cell tower didn't need a fiber connection? What if it just beamed its traffic to the switching center wirelessly? Dreams within dreams.

And then what if that switching center was actually located on a satellite? Or a balloon? Dreams within dreams within dreams!

Now, I don't want to go too far along this line of reasoning, mainly because there aren't many network technicians who do -- at least in the United States. But in other countries? The story is a little different.

According to a report last year by Ericsson, 40% of backhaul connections are expected to be based on wireless technology by 2023. And the standards group ETSI recently reported that wireless backhaul technologies serve more than 50% of the total cell site connections worldwide today. "They are apparently key solutions to address demands of mobile access networks at fast pace and in an economical way," ETSI reported of those wireless backhaul links.

As with most things though, the situation is a little different here in the United States. "We estimate North America is close to 26%" in its usage of wireless backhaul, wrote Jimmy Yu of research firm Dell'Oro.

But how might that situation change as we move into a 5G future?

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Speeding up wireless backhaul
Some are firm believers in a wireless backhaul future. "Many of our customers have asked us if we think microwave transport can handle the demands of a 5G radio access network," wrote Shane McClelland, head of transport in North America for equipment vendor Ericsson. (Microwave is often used as a synonym for wireless when discussing backhaul.) "The answer is yes."

"It's the customer's decision what they want to use," acknowledged Hans Mähler, head of microwave systems at Ericsson. However, he added: "What we want to show is that there’s a really good alternative to fiber."

Mähler is referring to a recent test Ericsson conducted with Deutsche Telekom to show off a commercial wireless backhaul link running at 40Gbps across a distance of around 0.87 miles by combining two 2GHz millimeter wave (E-band) channels, with latency of less than 100 microseconds (that's 0.1 milliseconds). And in case you're wondering: Yes, those metrics are impressive.

"While fiber is an important part of our portfolio, it is not the only option for backhaul," said Alex Jinsung Choi, SVP of strategy and technology innovation for Deutsche Telekom, in Ericsson's press release about the test.

(It's worth pointing out here that Ericsson definitely has skin in the game -- according to Dell'Oro, the top three vendors for wireless backhaul products in North America in the first nine months of 2018 were Nokia at 30% market share, followed by Aviat at 16% and Ericsson at 10%.)

Wireless backhaul "is no revolutionary technology... It's really a known technology,” said Ericsson's Jonas Hansryd, head of the company's microwave and millimeter-wave research, adding that wireless backhaul continues to improve as new wireless technologies -- including some of the elements in the 5G standard -- hit the market.

Further, Hansryd explained, Ericsson will likely be able to get even better performance in the future when it applies higher spectrum bands like the W Band (100 GHz) and the D Band (150 GHz) and additional wireless technologies like MIMO to wireless backhaul connections.

Incredibly, Ericsson's Hansryd and Mähler explained that wireless backhaul can even support lower latency than fiber backhaul. Meaning, if you want super duper low latency speeds, you actually want to use wireless backhaul, and you don't want to use fiber.

"Free air is almost the same speed as light, but if you take light in another medium, like glass [in a fiber connection], it's lower, based on the diffraction index," Mähler said, adding that the theoretical maximum measurement of latency across 10 km of fiber would be about 50 microseconds, whereas wireless backhaul would lower that to 30 microseconds across the same distance.

"All the big stock markets, like for instance between Chicago and New York … for where you need to have a really low latency when you have a remote service that is doing the buying and selling, they are going over microwave just to have the lowest latency." Hansryd added.

So wireless backhaul is ultimately better than fiber backhaul, right? Well, not really, at least according to most top US operators.